Re: [PATCH v2 16/17] intel_iommu: Introduce a property to control FS1GP cap bit setting

[Yi Liu]

On 2024/8/5 14:27, Zhenzhong Duan wrote:
> When host IOMMU doesn't support FS1GP but vIOMMU does, host IOMMU
> can't translate stage-1 page table from guest correctly.

this series is for emulated devices, so the above statement does not
belong to this series. Is there any other reason to have this option?

> Add a property x-cap-fs1gp for user to turn FS1GP off so that
> nested page table on host side works.

I guess you would need to sync the FS1GP cap with host before reporting it
in vIOMMU when comes to support passthrough devices.

> This property has no effect when vIOMMU isn't in scalable modern
> mode.
>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
> ---
>   include/hw/i386/intel_iommu.h | 1 +
>   hw/i386/intel_iommu.c         | 5 ++++-
>   2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/include/hw/i386/intel_iommu.h b/include/hw/i386/intel_iommu.h
> index 650641544c..f6d9b41b80 100644
> --- a/include/hw/i386/intel_iommu.h
> +++ b/include/hw/i386/intel_iommu.h
> @@ -308,6 +308,7 @@ struct IntelIOMMUState {
>       bool dma_drain;                 /* Whether DMA r/w draining enabled */
>       bool dma_translation;           /* Whether DMA translation supported */
>       bool pasid;                     /* Whether to support PASID */
> +    bool fs1gp;                     /* First Stage 1-GByte Page Support */
>   
>       /*
>        * Protects IOMMU states in general.  Currently it protects the
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index 9e973bd710..d7e7354db4 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -3778,6 +3778,7 @@ static Property vtd_properties[] = {
>       DEFINE_PROP_BOOL("x-pasid-mode", IntelIOMMUState, pasid, false),
>       DEFINE_PROP_BOOL("dma-drain", IntelIOMMUState, dma_drain, true),
>       DEFINE_PROP_BOOL("dma-translation", IntelIOMMUState, dma_translation, 
> true),
> +    DEFINE_PROP_BOOL("x-cap-fs1gp", IntelIOMMUState, fs1gp, true),
>       DEFINE_PROP_END_OF_LIST(),
>   };
>   
> @@ -4506,7 +4507,9 @@ static void vtd_cap_init(IntelIOMMUState *s)
>       /* TODO: read cap/ecap from host to decide which cap to be exposed. */
>       if (s->scalable_modern) {
>           s->ecap |= VTD_ECAP_SMTS | VTD_ECAP_FLTS;
> -        s->cap |= VTD_CAP_FS1GP;
> +        if (s->fs1gp) {
> +            s->cap |= VTD_CAP_FS1GP;
> +        }
>       } else if (s->scalable_mode) {
>           s->ecap |= VTD_ECAP_SMTS | VTD_ECAP_SRS | VTD_ECAP_SLTS;
>       }

--
Regards,
Yi Liu